diffame

A diff tool that understands your code.

Most diff tools compare files line by line. diffame parses your code into an AST with tree-sitter, matches nodes structurally, and produces a minimal edit script that tells you what changed, not which lines.

Move a function 200 lines down? One move-tree action instead of walls of red and green. Rename a variable? A single update-node, instead of a scattered shotgun blast across the file.

Install

cargo install --path .

Or with make:

make build
sudo make install

Quick start

diffame old.rs new.rs                   # side-by-side terminal output
diffame old.py new.py -f TEXT           # compact text summary
diffame config.json data.json -f JSON   # machine-readable JSON

Language is auto-detected from the file extension. For extensionless files (Dockerfile, Makefile, …) detection falls back to the filename. Use -l to override:

diffame a.txt b.txt -l py              # treat as Python

Use as git diff

Drop diffame in as your external diff driver and get structural diffs everywhere git shows you a diff:

git config --global diff.external diffame

That's it. git diff, git show, git log -p — all structural now.

To use it selectively:

GIT_EXTERNAL_DIFF=diffame git diff

Supported languages

60+ languages out of the box, including C, C++, C#, CSS, Dart, Elixir, Elm, Erlang, Fortran, GDScript, GLSL, Go, GraphQL, Groovy, Haskell, HCL, HTML, Java, JavaScript, JSON, Julia, Kotlin, LaTeX, Lua, Makefile, Markdown, Nix, Objective-C, OCaml, Pascal, Perl, PHP, PowerShell, Prolog, Protocol Buffers, Python, R, Racket, Ruby, Rust, Scala, Scheme, Solidity, SQL, Swift, TOML, TypeScript, Verilog, XML, YAML, Zig, and more.

Files with unrecognised extensions gracefully fall back to line-level diffing, diffame never refuses work.

Output formats

Flag	Description
-f SIDE	Side-by-side coloured terminal output (default)
-f TEXT	Compact text summary of actions
-f JSON	Machine-readable JSON with full match and action data

Options

Flag	Description
-l EXT	Override language detection (e.g. rs, py, js)
--max-file-size N	Max input size in bytes (default: 100 MB, 0 = unlimited)
--parse-timeout N	Parser timeout in seconds (default: 60, 0 = unlimited)

How it works

diffame implements the SimpleGumTree algorithm (Falleri & Martinez, ICSE 2024) in three phases:

1. Parse: tree-sitter builds a concrete syntax tree for each file.
2. Match: a top-down pass anchors identical subtrees; a bottom-up pass recovers container-level matches via Dice similarity.
3. Edit script: a Chawathe-style generator emits the minimal set of insert, delete, update, and move actions.

Development

make check       # fmt + clippy + tests
make test        # tests only

License

See LICENSE.md.